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Today, NASA released another poster in its wonderful ‘Exoplanet Travel Bureau‘ series. I’ve been a big fan of these prints since their inception; a fun and colorful outreach project that captures the diversity and exotic nature of these newly discovered worlds. However, they could be interpreted as more than just a NASA public relations project. If we consider art as a particular subjective interpretation of reality, subject to the fads, fashions and cultural context of the time, then these posters actually say quite a bit more!

They not only portray our early depictions of these enigmatic worlds, but our interpretations of what these planets may be like also sheds some light on our view of ourselves and the future. All the posters have a clearly evident retro-futuristic theme. A view of the future, but from the past. From the font choices, fashions and colour schemes, these posters are depicting the future of humanity, but through optimistic eyes of 1960s design, when flight and space exploration were developing at extraordinary rates, and holidaying on the Moon or Mars seemed only years away. By drawing on retrofuturism and space-age pop-art consumerism, the artists are trying to capture the anticipation and optimism of mid-20th century space science, and focus that enthusiasm on the hunt for Earth-like worlds, perhaps drawing parallels between the rate of planet discovery and that of aeronautics and space exploration during the 60s.

PSO J318.5-22 – Where the Nightlife Never Ends

The newest poster in the series depicts exoplanet PSO J318.5-22, a ‘rogue’ planet that has been ejected from its star system and is now sailing through interstellar space, but has since been turned into a party location by our intrepid descendants. To be honest, I really like this print. The throw-back to 1960s retro-futurism is undeniable, and this poster oozes cool and class – an elegant couple in minimalist spacesuits step out into the perpetual nightlife of a rogue exoplanet, a world so bizarre and strange that a few years ago the very idea of would have sounded preposterous. But here we are, turning an astronomical absurdity into a planetary-scale nightclub, all the while looking suave and beautiful as only humans can do. The simple duality of colors really capture the cold, cool and classy vibe, using blues, purples and silvery hues that gleam like auras off our descendants’ ‘nightclub-in-space’ regalia. In the background, figures stand suspended what appears to be a walkway along one of the planet’s icy rings, as more spaceships replete with party-goers arrives in sequence.

The three other posters in the series also adhere to a similar visual style. The print for Kepler-186 f depicts a couple exploring the striking red vegetation of this planet, the first Earth-size planet discovered in the potentially ‘habitable zone’ around another star. Its host star, Kepler 186, is a red dwarf, a much smaller star that emits more light in the red and infra-red portion of the electromagnetic spectrum than our Sun, and it is thought that if photosynthetic organisms were to exist on the surface of Kepler 186 f, they would be red in colour to exploit this fact. An interesting aspect of this poster is the white picket fence, a staple of American suburban utopia, that separates the green and red vegetation thereby accentuating the ‘grass is greener’ trope. Here, Earth-bound familiarity is juxtaposed against the alien backdrop of red foliage, and is proof that no matter how weird or exotic these worlds may be, the power of human culture will eventually make even the strangest of environments familiar to us.

When considering the artists’ interpretation of Kepler-16b, it is clear that the binary star system is the draw here. The unusual stellar architecture of this world would indeed make for a stunning double-sunset. Often considered a romantic activity best shared as a couple on Earth, here a single human figure enthralled by the graceful choreography of the binary is accompanied by two shadows instead. Although likely much too cold for life, Kepler 16b is portrayed in familiar desert tones of ochra and red, perhaps reminiscent of planets in binary systems in popular culture.

Experience the Gravity of a Super Earth

So what if HD 40307 g is eight times as massive as the Earth? We can turn this to our advantage, and thrill-seeking human skydivers are invited to plunge at incredible speeds through its (probably) thick gaseous atmosphere. Why? Because we can. Because we’re humans and evidently the whole galaxy is our playground.

The fact we know relatively little about these planets actually helps in this case, as imagination and artist license can run rampant. Significantly, these prints frame these worlds as utilitarian or ‘useful’, but not in the traditional economic or scientific sense. They’re useful and subservient to a human species so technologically advanced that even our recreation and tourism is now planetary in scale. There’s not much science being depicted, and that’s fine. These are travel posters for the future middle-class, an invitation to come for the exotic sights and stay for the booze, hiking or skydiving. The limited depiction of ‘life’ in these posters is somewhat unimaginative – a few red trees and the tinge of green on a continent, but I think that’s for the best at this stage. Overly stylized images of alien life would detract from the fact that humans are as much the focus in these posters as the alien planets.

The fact that we’re portrayed as out there using entire worlds for our recreation and fun speaks to the optimism of the search for extrasolar planets, and is well mirrored by the retro style employed by the artists. Unfortunately, being able to travel to these worlds is, in reality, completely unfeasible with contemporary technology, which makes the promises of lavish parties in deep space somewhat bittersweet. Nevertheless, I hope that NASA continues to publish posters in this series, and I look forward to seeing their next effort!

There were two kinds of landscape characteristic of the inner planets of the Sun: the purposeful and the desolate.

Stanislaw Lem – Fiasco (1986) [Ch.1, tr. Michael Kandel]

A loose rock tumbles slowly down a slope in a lonely valley on Mars. The hill of its origin seems unfamiliar and alien – it is more crimson and notably steeper than any rise on Earth due to Mars’ oxidizing environment and lower gravity. A loose conglomerate of ruddy scree, it seems completely devoid of life. The rock, idle in its elevated resting place for perhaps eons, now dislodged by a chance landslide caused by a violent Martian windstorm, rolls to a stop in a new location in the dry valley below. No human eyes have ever seen this boulder, no one has sat atop it to survey the panorama of the valley where it sat, or pounded it with a rock hammer to determine its composition, or crudely scrawled their initials into its surface in an attempt to immortalize a teenage love affair. What purpose, if any, does this boulder serve? Life cannot shelter beneath it or break it down for nutrients because no life exists on this frigid, desiccated planet. It inhabits an exclusively abiotic world, and whilst it will be shaped by powerful winds into exotic and unfamiliar forms, it will eventually be blown to dust by the continual onslaught of sandstorms, dissipating gradually, grain by grain, into the chaotic atmosphere. The universe seems no richer for its passing.

An alien world? Actually, this is the Atacama Desert in Chile, possibly the world’s oldest desert and one of the driest places on the planet. (via i09.com/Benjamin Dumas)

Desolation is a ubiquitous feature of the solar system. From the barren, scorched and pockmarked surface of Mercury, to the icy solitude of the gas giants, and out to the lonely minor planet Pluto in its long, dark trundle around the Sun, these are entire worlds devoid of life and the patient sculpting of natural process we are so familiar with on Earth. Their terrain is of great interest scientifically, but it is obvious that these are worlds very different to our own. They lack a certain something, an inherent dynamism that it seems only biology can imbue. They seem alien, and they are in some sense, but this feeling of other-worldliness issues forth from the unfamiliar landforms and empty horizons, broken here and there by topographies of pure abiological physicality. Nothing about these geographies serves a ‘purpose’. The craters of Mercury, or Mars, or any of the moons of Jupiter or Saturn, stand magnificent in their grandeur, but alone in the emptiness of space: many will never be explored, never investigated, chaotic in their form and distribution, but ultimately meaningless in their existence. It is my expectation that if we were to find another planet on which life had a foothold, that world would seem somehow more familiar to us, if undoubtedly exotic and bizarre, than a planet entirely devoid of biology.

This lack of purpose, of meaning, is obviously an inherently human concept, and whilst it results in an obvious planetary dichotomy (as illustrated by the quote above), it is this contrast that should provide us with perspective on our own planet and a greater appreciation for even the smallest action borne from the ancient, intimate dance between life and our world, choreographed by natural selection and honed by a run lasting billions of years. For if we consider these alien features to be meaningless and purposeless, it follows that the only ‘purpose’ that exists is that which began on Earth, and which emanates now ever outwards, shaping, and in some cases, biasing, our view of these barren worlds. Meaning is a concept that we as humans can and do impose upon desolate landscapes. We name features on distant planets, we photograph their lonely surfaces and seek explanations for their existence, but only as an aside in our quest for a greater understanding of our place and purpose. Even here on Earth we occupy the least biologically productive environments, sometimes for science, or for economic gain, or just for the challenge, but by our very presence in these once vacant landscapes, we provide a center of purpose. The once empty environment now provides a backdrop to the human drama, an extension of the boundless stage on which we carry out the acts of our lives; a silent witness to hours, days or years of collective human strife and trivialities. But is this really all meaning is? An inherently dichotomous characteristic of place that only exists relative to biology’s insight or attention?

In searching for a word to convey this sense of emptiness, of this abiotic ‘nothingness’, the limitations of terrestrial linguistics shaped by our Earth-bound experiences and history are revealed, and the true magnitude of the desolation – often global, near complete – remains difficult to comprehend and to express cogently. A world without any ‘meaning’, any direction, any sense of teleological drive. An environment surrendered to entropy and shaped by chaos and the haphazard actions of an abiotic ‘nature’. This is a nature unbounded by the necessities of life, in which soils and rocks remain untouched by biology but are instead molded, as clay in the hands of an inanimate potter, by purely physical processes: wind, fluids, irradiation and planetary tectonism. It seems that these are the environments most favored by the universe as they litter our solar system, and almost certainly exist around billions of other stars in our galaxy and beyond. Can it really be that an entire galaxy could exist in this state of meaningless stasis? Barren, empty reaches awaiting the arrival of life to imbue meaning upon the void?

It is possible that humans are the only intelligent observer species ever to have arisen in this galaxy. If that is the case, we have a great responsibility, not only to preserve our planetary sanctum for future generations and to continue to unravel the esotericisms of the universe, but to further safeguard our existence as the fount, the point source, of absolute meaning. The universe, it seems, is indifferent to our struggles, but we can elevate ourselves above the insignificant by our individual introspection and collective scientific extrospection.

Everyone trusts those great sages of our times, those for whom the intricate secrets of the universe are revealed by the night sky. As wise celestial engineers, the mechanics of the cosmos are obvious to them, the connections between the astronomical and the interpersonal are one and the same. These are people fluent in the language of the stars and skilled at interpreting their enigmatic relationship with humanity, akin to the unfurling of a stellar map of our collective psyche. Scholars all, who undertake years of dedicated study of ancient tomes going back hundreds of years, they have peered into the windows of our souls and seen the nuclear furnaces of the stars themselves.

I’m talking, of course, about astrologers. These wise, charitable, true scientists of our age, who dispense this precious knowledge for only the price of a premium-rate phone call or a column in a lifestyle magazine, to any and all comers. Can you think of a more noble profession?

It pains me however, as a relative newcomer to the field, to note that our astrological maps may be somewhat incomplete! Whilst the stars and constellations – whose graceful dance through our personal lives can be traced with ease by gifted astrologers – are relatively fixed in their positions (on human timescales), those charlatan astronomers have since discovered many, many more planets than the astrological academy may be aware.

Of course, let us not forget the effect of angry Mars on your unwavering passion to join the military, or that of powerful Pluto on your impending rebirth, kidnapping, or initiation into an underground crime syndicate 1. But what of the 1800 exoplanets discovered in the past decade or so? What of their effects on the minutia of your slow, inconsequential trudge to the grave? Well, thankfully, I’ve spent literal minutes conducting my own research on the astrological importance of some of these bodies, and now feel as qualified as any astrologer out there to suggest that you make important and possibly life-changing decisions based on the information I am about to provide to you 2.

Here are my predictions for the first four signs! More will follow soon of course.

(Or, alternatively, you could send a text message which will be charged at standard rates, plus £3.50, or visit my pop-up and clickbait-infested website below.)

Sagittarius

The constellation Sagittarius is positively awash with exoplanet-hosting stars, so hold on to your tarot cards because the astrological energy emanating from this sign may well disrupt your centre of balance if this month. HD 179949 b is a ‘hot-Jupiter’ – a massive planet orbiting very close to its parent star, which moves into the sign this week. Like this tumultuous world, you’re feeling increasingly resistant to spectroscopic analyses of your atmosphere, and are keeping evidence of titanium and vanadium oxides close to your chest, possibly to secure a promotion at work. This might seem to be a good strategy now, but your low bond albedo and furnace-like temperatures may make you hot under the collar – a prime target for infrared studies.

Capricorn

This month you may notice a feeling of cold eccentricity creeping into the trivialities of your everyday life. This is probably because of the effect of HD 204941 b on the goat sign this month – a frigid Neptunian planet with an off-center orbit who seems destined to cause a cold-spell in your love life. Detected by the sensitive HARPS instrument, like this planet you need to warm up to those close to you, especially if they’re astronomically massive spheres of super-heated plasma undergoing nuclear fusion, and accept that your radial velocity is discernible from light years away. You have to learn to embrace it and move on! Try sublimating a relaxing herbal or chi tea into your chaotic atmosphere as you near aphelion to help you unwind.

Aquarius

Good news! You may find yourself appreciating your relationships with your family members this month. The red-dwarf Gliese 876 is ascendant in this sign and like its extended family of four exoplanets, you’ll notice your loved-ones adopting a stable, coplanar Laplace resonance of 1:2:4, which will bring you neither further away nor any closer together, for the next 4 billion years at least. Be aware of co-workers and friends however, who like Gliese 876 itself will react in a highly unpredictable ways to your new-found stability, and will be prone to X-ray emissions. Steer clear girlfriend!

Pisces

Pisces is inundated with exoplanets, all of whom are jostling and vying for an chance to directly affect the fleeting existence of a billion apes on a tiny planet several light years distant. Can you not feel them? This month, like the gravitational interaction between Saturn-sized exoplanet HD 3651 b and its distant brown dwarf companion, you’ll feel like people on your extremely distant peripheries are disrupting your already highly eccentric orbit as a Pisces over the coming weeks. Just as NASA’s Spitzer Space Telescope directly imaged this system in 2006, so you’ll have the opportunity to compare existing theoretical evolutionary models to these substellar naysayers as we near Christmas. Just ensure you take some time out of your 62 day year for yourself!

Well, that’s all for now exoplanet astrology fans, but not to worry, I’ll be back with my readings of the remaining signs once I’ve had a chance to adjust my flux capacitor and have rechecked my calculations. Until then, remember: the whole universe is watching you. All the time. Wherever you are, and what ever you’re doing.

This was a guest post by the worlds foremost exoplanet astrologer, Dr Jawbone Hyurns. Follow him on Twitter for regular astrological and exoplanetary updates!

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1 In case it wasn’t obvious by now, this post is satire. However, these particular statements are actually based on stuff found online, where it was claimed Pluto is the planet of terrorism, death, obsession and kidnapping. Pluto’s taking its demotion to minor planet pretty hard it seems, and the astrologers still haven’t caught up on its new classification. I did consider including references, but felt an ethical obligation not to provide traffic to these sites. I took a virtual bath afterwards.

There is a word in Japanese, Yūgen(幽玄), derived from the study of Japanese aesthetics with no English equivalent, that perhaps comes closest to describing the profound sense of the enormity of the cosmos: to despair and be humbled by the insignificance of the struggle against the indifference of the universe, whilst also appreciating the sad beauty of human suffering. I often find myself grasping for a word to describe this reaction when discussing astrobiology with people, other scientists or members of the public, who find the entire field incredibly depressing; who, at some level, acknowledge the futility of our search for meaning in the distant reaches of space. Some find the emotional burden too great to bear, triggering a minor existential crisis. “It’s better not to know”, they say, “Not to think about it. Besides, [insert reality TV show name here] is on!”

On one hand, who can blame them? It’s not like we’re expecting answers to many of The Questions that astrobiology and astronomy are trying to solve in our lifetimes. Science is a gradual process after all, and one that will last as long as there are still questions to be answered. The relative insignificance of our personal lives, our careers and relationships, cast against the enormity of the cosmos and separated by orders of magnitudes of space and time, so clearly presented, can prove a bit too much. The Astronomical Perspective can be overwhelming, and astronomy, as Carl put it, is a humbling experience. I’d like to adopt yūgen as a general descriptor of these feelings.1

Astrobiology is a scientific discipline practised from deep within in the realms of bounded rationality. These bounds stem from a definite, fundamental and detrimental lack of information about the system, as well as a possible cognitive and technological limitation in processing of the limited information available to us. We definitively lack the resources to arrive at an optimally rational conclusion regarding our place in the universe, the existence of suitably habitable environments elsewhere, and the possibility of life on other planets. And yet, we know we’re close. We suffer a kind of collective Dunning-Kruger effect regarding how little we know, and how little we know about how little we know. We’re approaching that greatest of unknowns, cobbling together a piecemeal scientific narrative as we go, but missing so many parts of the puzzle that it’s not even clear what it is we’re building. Yet, something innate drives us onwards. Some part of us that has always been, as if a distant memory or half-remembered dream, within our genetic luggage and passed on to us from pre-human ancestors.

The size of our brains relative to our body size (also known as the encephalization quotient (EQ)) has, in fact, gotten smaller in recent times, peaking ~30,000 years ago after 2 million years of expansive growth. I’ll leave the anthropologists to argue over why and what this means, but making some crude assumptions about intelligence and EQ we can assume, therefore, that our extremely distant ancestors may have gazed up at the canopy of the night sky and felt that same intangible yearning as we do. At least, there seems to be no cognitive reasons that they couldn’t have done so. Maybe it was even more pronounced by the gulf of knowledge that separates their knowledge of the cosmos from our own? The bright band of the Milky Way stretched out overhead, unobscured by pollution, but hidden by ignorance; an unknowable story waiting for a narrator, one that would not arrive in earnest for thousands of years. In the meantime, complex and anthropomorphic mythologies were borne and woven by the tapestry of human imagination and fuelled by our penchant for storytelling.

Perhaps, that sense of insignificance, that yūgen, was even more heart-wrenching in the very distant past when we were young, when our contemporary achievements in understanding of our place in the greater Story would seem unfathomable, akin to magic. Perhaps, yūgen has been a driving force in our history as long as we have existed? I’m not suggesting an evolutionary driver akin to bipedalism, but perhaps a minor constituent of the human story that contributed an unquantifiable edge to our tale. An ember burning near the edge of the campfire of humanity’s intellectual awakening, smouldering away throughout the ages whilst we built our temples and cities, waged our wars and battles, waiting for the spark of enlightenment to burst into an inferno of curiosity and discovery.

That’s why I’m optimistic about our search. Sure, we may not find any concise answers to the ‘big’ questions in our lifetimes, and we’ll probably always have that sense of yūgen when faced with incomprehensible enormity on galactic and light year-scales, but rather than hiding in the dark, we should embrace the feeling of astronomical despair and turn it into a creative force for discovery! If you don’t like being insignificant, find something that makes you significant. Yūgen will be passed on to the next generation of curious scientists and philosophers, and as it has done in the past, it will drive us on to more profound questions and more mysterious unknowns.

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1 If any Japanese speakers are reading this, please let me know if I’m using this word incorrectly – my understanding is that the context is important.

This is a guest post by David Wilson, a PhD student in the Astronomy and Astrophysics group at the University of Warwick, where he studies the remains of planetary systems around white dwarfs (see below!). He can be found on Twitter and blogs about various astronomy topics at Stuff About Space.

White dwarfs are dead stars, the burnt out carbon cores of stars like our Sun which have exhausted their hydrogen fuel; incredibly dense, incredibly hot balls of matter roughly the size of the Earth. Because of their high temperature, tens of thousands of degrees, all white dwarfs glow blue.

But the light from GD 29-38 wasn’t just blue. When it was split into a spectrum, separated into a rainbow of separate colours, there seemed to be something else there. Something shining with an infrared light, beyond the range of our eyesight.

Initially the discovers were excited, as the red light could have come from an orbiting brown dwarf, a mysterious object several times bigger than a planet but much smaller than a star. But both the white dwarf and the infrared source were pulsating slightly, periodically getting brighter and dimmer. If the red light was from a separate object, then it shouldn’t have pulsed in time with the white dwarf.

An asteroid plummets to its doom around the white dwarf GD 29-38. Studying the debris left from these asteroids can reveal the chemical composition of exoplanets. Image Credit: NASA

The spectrum also revealed metals in the white dwarf’s atmosphere, heavy elements like calcium, magnesium and iron. These were also out of place, as white dwarfs have such a strong gravity that anything heavier than hydrogen or helium should have sunk down into their cores long ago. The metals must be falling onto the white dwarf from the space around it- but how did they get there?

It took until 2003 for the origin of the mysterious infrared glow to be found, during which time many more white dwarfs with similar red spectra and metal polluted atmospheres were found. The explanation was that the infrared light is coming from a disc of dusty debris surrounding the white dwarf.

This debris was formed from the wreckage of an asteroid, leftover from when GD29-38 was a Sun-like star with its own system of planets. The dust in the disc rains down onto the white dwarf, explaining the metals we see in the atmosphere.

The spectrum of GD 29-38. Along the bottom is its wavelength, or colour, going from blue on the left to invisible infrared on the right. The vertical axis shows how bright the white dwarf is at each wavelength. The difference between the blue white dwarf and red dust cloud can be clearly seen. Image Credit: NASA

The story of how the debris disc got there is a result of the turbulent formation of the white dwarf. As it runs out of fuel a star swells up to a huge red giant, then blows away roughly half of its mass in an immense stellar wind, leaving the tiny white dwarf core.

With the gravitational force at its heart cut in two, the system of planets around the dying star is thrown into chaos. Planets begin to migrate outwards, trying to reach orbits twice as far away from the central star as before. As they do this, they risk coming into close contact with each other.

Some of the planets survive these encounters and carry on as they are. Others, especially when a big Jupiter sized planet is involved, are thrown out of the system into the depths of interstellar space. And some are scattered into the centre of the system towards the white dwarf.

These unlucky asteroids and dwarf planets fall in towards the white dwarf until they reach a point known as the tidal disruption radius. There the tidal force, the difference in gravitational pull between the parts of the asteroid nearest the white dwarf and the areas further away, becomes so great that the asteroid is ripped apart, forming the dusty debris disc that we see as an infrared glow.

The discovery of this process lead to an important conclusion. As the dust rains down onto the white dwarf it becomes visible to our telescopes. If we can measure what metals there are, and how much of each there is, then we can reveal the chemical composition of the asteroid or planet that formed the disc. We can ask, and answer, the question: “What are planets made of?”

Two decades ago we only knew about the eight planets in our solar system (Pluto was never a planet, it was just mislabelled). Now we know of over a thousand planets, new worlds orbiting hundreds of stars. Through our telescopes we can measure the size of these planets, what their masses are, and even in some cases get a glimpse into their atmospheres.

But we can’t find out what they’re made of, what the geology of these newly discovered planets is like. This means that we don’t know for sure if the way that the rocky planets are built in our solar system, the particular mix of iron, oxygen, magnesium, silicon and other chemicals that make up the Earth and its neighbours, is the way all planets are built.

The metal polluted white dwarfs form a perfect laboratory, presenting us with rocky objects that have broken apart into their chemical components. By observing as many as we can, we can begin to explore the chemical diversity of planets and planetary systems. We can see if the way our planets are built is the normal way to construct a planet, or whether Earth is even more unique than we thought.

To date we’ve discovered around a dozen white dwarfs with enough chemicals to compare their systems in detail with our own. So far, they look fairly similar to the Earth, a hopeful sign. But we need many more to truly explore this area, and over the next few years myself and others will be scouring the sky, using the Hubble Space Telescope above us and an array of telescopes on the ground. We will find more metal polluted white dwarfs, measure the chemicals of the planetary debris around them, and begin to explore in detail what things you need to build a planet.

This is a guest post by Euan Monaghan, a post-doctoral researcher in the Department of Physical Sciences at The Open University, where he studies the habitability of the subsurface of Mars. You can find him on Twitter.

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Astrobiology is the search for life elsewhere in the universe. When this search is focussed on a specific world, there’s a chance—quite a good chance it would seem—that this search will turn out to be fruitless; that there will be no life to be found except the terrestrial life we bring along with us in the process. But can we ever say for sure?

This piece is focussed on Mars, but the idea applies to all worlds targeted for astrobiological exploration. The particular habitats on Europa, Titan or Kepler-62e might be different to those found on Mars, but the question is the same everywhere: does this world host life?

Scientific progress has made the martians of our imagination progressively smaller and more insignificant. No longer the grand canal builders of old—no longer even considered to be multi-cellular—the optimistic amongst us imagine microbes in briny pockets kilometres beneath a hostile surface; their presence deep underground given away by a subtle disequilibrium in the gases of Mars’ tenuous atmosphere. If the martians are there, they’re in hiding.

As we gain a greater understanding of the geologic and climatic history of Mars, a subterranean biosphere doesn’t seem so unreasonable. While Mars was likely warm and wet long before the Earth was, it is also smaller and so cooled faster. It couldn’t hold onto a thick, warming atmosphere for long and so its surface water was gradually lost, both out into space and down into the planet’s interior, to be fixed within the structure of minerals, frozen as permafrost or trapped in groundwater aquifers beneath layers of ice. And as Mars cooled and the water descended, so did the planet’s habitable zone, until it was hidden from view.

Recurring slope lineae in Coprates Chasma may be due to active seeps of water; a clue to a possible subsurface biosphere? (Credit: NASA/JPL/University of Arizona, HiRise)

The habitability of any extra-terrestrial environment is estimated through the study of life adapted to extreme conditions on the Earth. This ‘envelope of life’, with its upper and lower boundaries of temperature, pressure, salt tolerance and so on, is expanding all the time. The relatively recent discovery of our own deep subsurface biosphere, as well as its remarkable diversity and extent, has broadened our concept of what we consider to be a habitable environment. It is with this ever-more subtle knowledge of our own world that we turn back to the planets in our search for life.

The next logical step in that search, for Mars at least, is a detailed study of its atmosphere. In early 2016 the European Space Agency will launch a mission to do just that: the ExoMars Trace Gas Orbiter (TGO) will perform a more comprehensive inventory of the martian atmosphere and the respective abundances of its gases than ever before. It is hoped that the results of this study will provide an insight into active processes occurring deep underground. But then again there is the very real possibility that the TGO will arrive in orbit and find no signs of life, however tentative. The null hypothesis—Mars is a barren world—would still stand. Should we then give up on our search, or do we commit time and resources to a strategy of ever more sophisticated astrobiological exploration, all the while striving to prevent accidental contamination by terrestrial life?

The inevitable moments when we decide to re-focus our search for life beyond the Earth should not be considered moments of pessimism. The universe has too much potential.

This is a guest post by Sean McMahon, a PhD student in the School of Geosciences at the University of Aberdeen. Sean’s research applies geological perspectives and techniques to astrobiological problems ranging from the origin and distribution of life in the universe to the origin of methane in the Martian atmosphere. Visit his excellent blog, Fourth Planet, for more on his research, his impressive space art and photography, and writings.

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“Though a planetary perspective is a magnificent and enriching thing, places, not planets, are the core of human experience. It is from places that we build our world.”

— Mapping Mars, Oliver Morton (2002)

“He stood thereby, though ‘in the centre of Immensities, in the conflux of Eternities,’ yet manlike towards God and man; the vague shoreless Universe had become for him a firm city, and dwelling which he knew.”

— The French Revolution: A History, Thomas Carlyle (1837)

Last year, in a car park in Aberdeen, I saw Jupiter through a telescope for the first time. What I saw was not the familiar red-spotted giant from the Nasa photographs, that great bronze bauble marbled with cream like artisan coffee—no. What I saw, through a gap in the Scottish clouds, was a pale round smudge with three white specks for moons. It was not dramatic but it was a strange and lovely moment. It reminded me that Jupiter, the other planets, and even the distant stars and galaxies, are no less real, no less here—albeit further away—than Scotland, clouds, car parks, and me. They are on the same map, sharing our geography, our humdrum commonplace reality.

In our eagerness to be inspired by astronomical imagery, we are often tempted to forget this fundamental sameness. Documentaries about the cosmos besiege us with spectacular graphics, rousing orchestral music and rapturous, lyrical narration. In the tradition of Carl Sagan, we are urged to adopt a “cosmic perspective”, in which the Earth dwindles to an insignificant1 “mote of dust suspended in a sunbeam”. Meanwhile, digital space art is reliving the Romanticism of 19th Century painting: balance, proportion and subtlety are abandoned in favour of vertiginous perspectives, extremes of colour and contrast, and sublime, mystical lighting: silhouetted planets disintegrate into vast purple nebulae bristling with crepuscular rays. Thus, it seems that an ecstatic, almost mythical vision of outer space, emphasizing above all its spiritual and aesthetic grandeur, has taken root in popular culture.

McMahon juvenilia. This is what I thought space looked like when I was 17. I have since changed my mind.

Maybe that vision has some role to play in attracting public interest to the space sciences. But paradoxically, it can make the “wonders of the universe” seem less accessible than ever; profound, ethereal, miraculous, even unreal. It bolsters the popularity of astrology by reinforcing the illusion that planets and stars are unfathomable, heavenly beings: much more plausible aids to divination than ordinary material things. Most worryingly, it can give the impression that space exploration is an esoteric spiritual quest, unrelated to ordinary human problems and unfit for serious attention from media, government or young, career-minded scientists.

Perhaps the “numinous” view of space reflects a deeper failure to grasp the implications of the Copernican Revolution. Somehow, I suggest, we still make some kind of basic ontological distinction between the heavens and the Earth2. Consequently, we are unable to feel truly embedded in our extraterrestrial environment, which remains a transcendent, detached and coldly beautiful space rather than a homely, material, lived-in place. The Apollo programme helped to bridge that gap for a generation, transforming the moon from an icon of celestial indifference into a humanly intelligible landscape—rather like a golf course, in fact, replete with bunkers, buggies, flags and footprints3. Revealingly, many people today find it easier to believe that the whole thing was a hoax.

The sharp, vivid photographs taken by NASA’s Curiosity Rover can have a similar effect, reminding us that the martian surface is a real place, not so different in appearance from the rocky deserts of Libya or the High Arctic. Despite our unsophisticated cultural relationship with outer space—a mixture of mythology, indifference and reverence—a crewed mission to Mars in the next thirty years now seems very likely. I hope that mission will allow the next generation to feel more at home in the universe, more fully at ease with the fact that even Milton Keynes4 is part of the Milky Way. What we stand to gain is not an exalted “cosmic perspective” but simply a richer, more expansive sense of place, of where it is that we live our lives.

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1 This strain of rhetoric characteristically fails to observe that human beings adjudicate the significance of the universe, not the other way around.

2 Douglas Adams exploited this confusion to humorous effect, juxtaposing ordinary things with cosmic phenomena: the “restaurant at the end of the universe,” the “whelk in a supernova” and so on; “you may think it’s a long way down the road to the chemist but that’s just peanuts compared to [the size of] space”.

3 Some readers will know that the American astronaut Alan Shephard did in fact play golf on the moon; two golf balls remain there.

4 Milton Keynes is an architecturally unprepossessing English town and home to the Open University, where much British space research has been conducted.

This is a guest post by Hugh Osborn, a PhD student in the Astronomy and Astrophysics group at the University of Warwick. Hugh’s research involves using transit surveys to discover exoplanets. Visit his excellent blog, Lost in Transits, for more on exoplanets, their detection and his research.

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In the 1890s Percival Lovell pointed the huge, 24-inch Alvan Clark telescope in Flagstaff, Arizona towards the planet Mars. Ever the romantic, he longed to find some sign of life on the Red Planet: to hold a mirror up to the empty sky above and find a planet that looked a little bit like home. Of course, in Lovell’s case, it was the telescope itself that gave the impression of life, imposing faint lines onto the image that he mistook for canals. But, with Mars long since relegated to the status of a dusty, hostile world, that ideal of finding such a planet still lingers. In the great loneliness of space, our species yearns to find a world like our own, maybe even a world that some other lineage of life might call home.

A hundred years after Lovell’s wayward romanticism, the real search for Earth-like planets began. A team of astronomers at the University of Geneva used precise spectroscopy to discover a Jupiter-sized world around the star 55-Peg. This was followed by a series of similar worlds; all distinctly alien with huge gas giants orbiting perishingly close to their stars. However, as techniques improved and more time & money was invested on exoplanet astronomy, that initial trickle of new worlds soon turned into a flood. By 2008 more than 300 planets had been discovered including many multi-planet systems and a handful of potentially rocky planets around low-mass stars. However, the ultimate goal of finding Earth-like planets still seemed an impossible dream.

In 2009 the phenomenally sensitive Kepler mission launched. Here was a mission that might finally discover Earth-sized planets around Sun-like stars, detecting the faint dip in light as they passed between their star and us. Four years, 3500 planetary candidates and 200 confirmed planets later, the mission was universally declared a success. Its remarkable achievements include a handful of new terrestrial worlds, such as Kepler-61b and 62e, orbiting safely within their star’s habitable zones. However, despite lots of column inches and speculation, are these planets really the Earth 2.0s we were sold?

While such worlds may well have surfaces with beautifully Earth-like temperatures, there are a number of problems with calling such worlds definitive Earth twins. For a start the majority of these potentially habitable planets (such as Kepler-62e) orbit low-mass M-type stars. These are dimmer and redder than our Sun and, due to the relative distance of the habitable zone, such planets are likely to be tidally locked. The nature of such stars also makes them significantly more active, producing more atmosphere-stripping UV radiation. This means, despite appearances, ‘habitable’ planets around M-dwarfs are almost certainly less conducive to life than more sun-like stars.

Even more damning is the size of these planets. Rather than being truly Earth-like, the crop of currently known ‘Habitable planets’ are all super-Earths. In the case of Kepler’s goldilocks worlds, this means they have radii between 1.6 and 2.3 times that of Earth. That may not sound too bad, but the mass of each planet scales with the volume. That means, when compression due to gravity is taken into account, for such planets to be rocky they would need masses between 8 and 30 times that of Earth. With 10ME often used as the likely limit of terrestrial planets, can we really call such planets Earth-like. In fact, a recent study of super-Earths put the maximum theoretical radius for a rocky planet as between 1.5 and 1.8RE, with most worlds above this size likely being more like Mini-Neptunes.

So it appears our crop of habitable super-Earths may not be as life-friendly as previously thought. But it is true that deep in Kepler’s 3500 candidates a true Earth-like planet may lurk. However the majority of Kepler’s candidates orbit distant, dim stars. This means the hope of confirming these worlds by other techniques, especially tiny exo-Earths, is increasingly unlikely. And with Kepler’s primary mission now ended by a technical fault, an obvious question arises: just when and how will we find a true Earth analogue?

Future exoplanet missions may well be numerous, but are they cut out to discover a true Earth-like planet? The recently launched Gaia spacecraft, for example, will discover hundreds of Gas Giants orbiting Sun-like stars using the astrometry technique, but it would need to be around a hundred times more sensitive to discover Earths. New ground-based transit surveys such as NGTS are set to be an order of magnitude better than previous such surveys, but still these will only be able to find super-Earth or Neptune-sized worlds.

The Transiting Exoplanet Survey Satellite (TESS) (space.mit.edu)

Similarly, Kepler’s successor, the Transiting Exoplanet Survey Satellite which is due to be launched in 2017, will only be able to find short-period planets with radii more than 50% larger than Earth. HARPS, the most prolific exoplanet-hunting instrument to date, is also due for an upgrade by 2017. Its protégée is a spectrometer named ESPRESSO that will be able to measure the change in velocity of a star down to a mere 10cms-1. Even this ridiculous level of accuracy is still not sufficient to detect the 8cms-1 effect Earth’s mass has on the Sun.

So despite billions spent on the next generation of planet-finders, they all fall short of finding that elusive second Earth. What, precisely, will it take to find this particular Holy Grail? There is some hope that the E-ELT (European-Extremely Large Telescope), with its 35m of collecting area and world-beating instruments will be able to detect exo-earths. Not only will its radial velocity measurements likely be sensitive enough to find such planets, it may also be able to directly image earth-analogues around the nearest stars. However, with observing time likely to be at a premium, the long-duration observations required to find and study exo-earths could prove difficult.

Alternatively, large space telescopes could be the answer. JWST will be able to do innovative exoplanet research including taking direct images of long-period planets and accurate atmospheric spectra of transiting super-Earths and giants. Even more remarkably, it may manage to take spectra of habitable zone super-Earths such as GJ 581d. But direct detection of true Earth-analogues remains out of reach. An even more ambitious project may be required, such as TPF or Darwin. These were a pair of proposals that could have directly imaged nearby stars to discover Earth-like planets. However, with both projects long since shelved by their respective space agencies, the future doesn’t look so bright for Earth-hunting telescopes.

After the unabashed confidence of the Kepler era, the idea that no Earth-like planet discovery is on the horizon may come as a surprisingly pessimistic conclusion. However not all hope is lost. The pace of technological advancement is quickening. Instruments such as TESS, Espresso, E-ELT and JWST are already being built. These missions may not be perfectly designed to the technical challenge of discovering truly Earth-like planets, but they will get us closer than ever before. As a civilisation we have waited hundreds of years for such a discovery; I’m sure we can hold out for a few more.

Around this time every year, the Earth, on her year long trundle around the Sun, passes through the Perseid cloud of cometary debris. The resulting month long encounter produces arguably the most prolific and spectacular meteor shower for northern observers – the Perseids. As many as 100 “shooting stars” an hour may be visible at its peak in mid-August and the shower is eagerly awaited by sky-gazers for it’s dazzling and reliable display of colourful meteors and fireballs.

The source of the Perseids is dust and debris contained in a relatively dense ‘cloud’ impacting the upper atmosphere of the planet and burning up due to rapid deceleration due to increased aerodynamic drag. The shower has been observed for millennia, the first recorded sighting was in 69 BC, and most of the dust and debris responsible for the shower was pulled off a comet a thousand years ago. The particles that produce this astronomical light-show are generally tiny, on the order of centimetres, and pose little threat to the Earth below. However, the same cannot be said for their parent, comet Swift-Tuttle.

Comet Swift Tuttle (designation: 109P/Swift–Tuttle) is a typical Halley-like long period comet. It tears through the inner solar system when nearing the closest approach of its 133 year orbit around the Sun; an orbit that takes it out 12 AU past Pluto to 51 AU, and all the way back again. Its last close encounter with Earth was in 1992, and it won’t return until 2126.

For a while following its rediscovery in 1992, almost 10 years away from its expected position, the orbital evolution of the comet was not well constrained and there was considerable cause for alarm when it was estimated to be on a collision course with Earth in 2126. Concern was justified: its nucleus is 26km in diameter, considerably larger than the 10 km impactor that is thought to have caused the Cretaceous-Paleogene (K-T) mass extinction event 65 million years ago. However, reanalysis of ancient records of observations and improved calculations that included the effects of nucleus evaporation confirmed that the comet is on a very stable orbit and poses little threat to Earth for the next 2000 years.

That said, in a 1997 book by South African/American radio astronomer Gerrit Verschuur, comet Swift-Tuttle was described as the most dangerous object known to man for it’s ability to cause catastrophic damage if it was to impact the Earth. An exceptionally close encounter is expected in 4479, bringing Swift Tuttle to within 0.03 AU (approximately 4 million km) of the Earth – roughly 10 times the mean Earth-Moon distance. Travelling at a relative velocity of 60 km per second, Swift-Tuttle would unleash the equivalent of a devastating 3.2×1015 tons of TNT upon impact – 27 times the energy of the K-T impactor. For comparison, the largest nuclear weapon ever detonated was a ‘mere’ 50 megatons (106). It would very likely cause huge loss of life across the planet and result in a mass extinction unlike any known previously, whilst placing unbridled pressure on the capacity for human civilisation to recover. If the initial impact was survived, tsunamis, wildfires, earthquakes, years of darkness and a toxic atmosphere would follow. Harvard astrophysicist John Chambers estimates the chance of collision in 4479 to be 1 in 1,000,000. Best of luck to our descendants 2467 years from now!

It is worth bearing this in mind when you gaze up over the next few nights to witness the magnificent sight of the ancient dust of this comet burning up in our atmosphere, for one day their parent may put on a somewhat more spectacular, if devastating, show.

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Awards

Short-listed for the Wellcome Trust Science Writing Prize 2012:
For this article.

Welcome!

Astrobiology and the study of planets throughout the galaxy deal with some of the most profound questions regarding our existence: where did we come from, are there other worlds like ours out there, and are we alone?

I don't profess to be able to answer these questions, but that doesn't stop me from cobbling together some loosely coherent thoughts to share with interested readers. I find it helps me to maintain a cosmic perspective.

I completed a PhD in the Centre for Ocean and Atmospheric Science at the University of East Anglia in 2015, broadly focussed on planetary habitability, astrobiology, and global biogeochemical cycling on Earth.

I am also a committee member of the Astrobiology Society of Britain. Visit the ASB website for more information about astrobiology in the UK:

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